Lazyness: I didn't want to have to walk to the cart and turn in on to find out what the battery voltage is.
Accuracy: I wanted to monitor the actual battery pack voltage rather than switched voltage at the keyswitch.
The switched voltage at the keyswitch on a stock PDS stock passes through 6 plug/jack connections and 3 sets of switch contacts in addition to passing through the printed circuit boards in the controller twice.
Veristility: By having the + & - leads ran into the battery compartment, I can easily use the dash mounted DVM to monitor any voltage I want to monitor.
Just disconnect the + lead from B+ at the battery back and add an extension wire with alligator clips.
Or disconnect and extend both wires from the meter to monitor point to point voltages, such as the voltage between the A1 & A2 studs on the motor.
It only has 0.1V resolution, but that is close enough to determine if one (or more) battery is dropping under load significantly more than the others.
Safety: My cart was parked so I could see the meter while leaning on my back porch rail, smoking a stinky cigar (SWMBO's description of my favorite cigars with Oscuro leaf wrappers) and the Pro-Tech on-board charger was plugged in. I noticed the pack voltage was 48.5V when it should have been 39.4V (Float charge level).
The Pro-Tech charger had failed and was pumping all the amps it could possible pump into the battery pack.
Fortunately, I noticed it before the plates were expose, but the pack did take more than a gallon of distilled water.
Ironically, that overcharging episode probably helped the old batteries.
I've since gone to DPI chargers, but I still keep an eye on the pack voltage.
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Yes, my DVM type SoC meter has three red LED seven segments displays in it.